Series-resonance oscillator

ABSTRACT

An oscillator circuit ( 100 ) comprises a first tank circuit (T 1 ) comprising an inductive element (L) and a capacitive element (C) coupled in series between a first voltage rail ( 14 ) and a first drive node ( 12 ). A feedback stage (F) is coupled to a first tank output ( 13 ) of the first tank circuit (T 1 ) and to the first drive node ( 12 ). The feedback stage (F) is arranged to generate, responsive to a first oscillating tank voltage present at the first tank output ( 13 ), a first oscillating drive signal at the first drive node ( 12 ) in-phase with a first oscillating tank current flowing in the inductive element (L) and the capacitive element (C), thereby causing the oscillator ( 100 ) to oscillate in a series resonance mode of the inductive element (L) and the capacitive element (C).

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/417,040, filed Jan. 23, 2015, which is a 35 U.S.C. §371 nationalphase filing of International Application No. PCT/EP2014/057873, filedApr. 17, 2014, the disclosures of which are incorporated herein byreference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates to an oscillator circuit, a method ofoperating an oscillator circuit, and a wireless communication devicecomprising an oscillator circuit.

BACKGROUND TO THE DISCLOSURE

Harmonic oscillators known in the art, and implemented in an integratedcircuit chip, comprise an inductor and a capacitor, generally known as atank, operating at a resonance frequency of the tank. Typically, such anoscillator injects a pulse waveform into the tank, which filters outhigher current harmonics and generates a sinusoidal voltage waveform atits output. The tank comprises the inductor and capacitor coupled inparallel, and operates in a parallel resonance mode, where the parallelimpedance, that is, the impedance of the inductor and capacitor coupledin parallel, is high, generating a relatively high oscillation voltagefrom a relatively low bias current.

In some applications, for example, in wireless communication apparatus,an oscillator is required that has an extremely low phase noise incombination with a low power consumption. Such a combination isdifficult to achieve, particularly if the available power supply voltageV_(dd) is low, as is often the case with present-day nanometrecomplementary metal oxide semiconductor (CMOS) processes. Increasing theoscillation voltage swing can reduce the phase noise of an oscillator.However, conventional oscillators are limited by the maximum voltageswing they can provide, which ranges from a peak single-ended voltage of2V_(dd), to 3V_(dd), the latter being possible in so-called class-Doscillators. Reducing the inductance of the inductor and increasing thecapacitance of the capacitor can also decrease the phase noise. However,if the required inductance is very small, for example, a few tens ofpicoHenrys, this approach can become difficult to manage due toparasitic inductances and resistances of the integrated circuit thatstart playing a dominant role. Furthermore, the quality factor of verysmall inductors is lower than for larger inductors, resulting in ahigher power consumption for a given phase noise level.

FIG. 1 illustrates a typical Clapp oscillator employing a parallelresonance mode. Referring to FIG. 1, the Clapp oscillator has a firsttank T_(A) comprising a first inductor L_(A) and a first capacitorC_(A). The first inductor L_(A) and the first capacitor C_(A) arecoupled in series to a drain of a first transistor Q_(A). For providinga differential tank voltage V_(OUT), the Clapp oscillator also has asecond tank T_(B) comprising a second inductor L_(B) and secondcapacitor C_(B). The second inductor L_(B) and the second capacitorC_(B) are coupled in series to a drain of a second transistor Q_(B). Thefirst and second transistors Q_(A), Q_(B) have theirs gates biased by aconstant bias voltage V_(DC). The Clapp oscillator is a current-modeoscillator, which means that the first and second transistors Q_(A),Q_(B) operate as transconductors, providing voltage-to-currentconversion, and delivering a large current to their respective first andsecond tanks T_(A), T_(B) without loading the tanks. Therefore, eachtransconductor must have high parallel impedance. Although the first andsecond tanks T_(A), T_(B) have series coupled inductors and capacitors,the Clapp oscillator does not oscillate at the series resonancefrequency of the series coupled inductors and capacitors. Instead, theClapp oscillator oscillates at a frequency that is determined by allreactive components in the tanks, including the capacitances between thedrain and source, and the source and ground, of the first and secondtransistors Q_(A), Q_(B). These capacitances are also represented inFIG. 1. For a given bias current supplied to sources of the first andsecond transistors Q_(A), Q_(B), the oscillation amplitude isproportional to the bias current and an equivalent parallel tankresistance. Therefore, for the current-mode Clapp oscillator with a biascurrent I_(BIAS) provided by first and second current sources I_(A),I_(B) illustrated in FIG. 1, the amplitude of the tank voltage V_(OUT)can be expressed as

V _(OUT) =k·I _(BIAS) ·R _(PEQ)  (1)

where R_(PEQ) is the equivalent parallel resistance of each of thetanks, which is proportional to the quality factor Q of each of thetanks, and k is a proportionality factor. In the Clapp oscillator, theparallel resistance of each of the tanks is deteriorated by the feedbackat the transistor source through the capacitive tap between drain andsource and source and ground.

There is a requirement for an improved oscillator.

SUMMARY OF THE PREFERRED EMBODIMENTS

According to a first aspect there is provided an oscillator circuitcomprising:

a first tank circuit comprising an inductive element and a capacitiveelement coupled in series between a voltage rail and a first drive node;and

a feedback stage coupled to a first tank output of the first tankcircuit and to the first drive node;

wherein the feedback stage is arranged to generate, responsive to afirst oscillating tank voltage present at the first tank output, a firstoscillating drive voltage at the first drive node in-phase with anoscillating tank current flowing in the inductive element and thecapacitive element, thereby causing the oscillator circuit to oscillatein a series resonance mode of the inductive element and the capacitiveelement.

According to a second aspect there is provided a method of operating anoscillator circuit, the oscillator circuit comprising a first tankcircuit comprising an inductive element and a capacitive element coupledin series between a voltage rail and a first drive node, the methodcomprising generating, responsive to a first oscillating tank voltagepresent at a first tank output, a first oscillating drive voltage at thefirst drive node, wherein the first oscillating drive voltage isin-phase with an oscillating tank current flowing in the inductiveelement and the capacitive element, thereby causing the oscillator tooscillate in a series resonance mode of the inductive element and thecapacitive element.

Therefore, the oscillator circuit is voltage driven and oscillates in aseries resonance mode. This enables a high amplitude of oscillation withonly a low power supply voltage, which enables a low phase noise.

The following embodiments provide different low complexity solutions forimplementing the oscillator circuit and method of operating anoscillator circuit.

The feedback stage may be arranged to generate the first oscillatingdrive voltage having a substantially rectangular waveform. This featureenables a switching device to be used, thereby enabling low powerconsumption.

In a first preferred embodiment of the oscillator circuit, the firsttank circuit may arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage in-phasewith the first oscillating drive voltage, and the feedback stage maycomprise a first driver arranged to generate, responsive to the firstoscillating tank voltage, the first oscillating drive voltage in-phasewith the first oscillating tank voltage. Likewise, a first preferredembodiment of the method may comprise generating the first oscillatingtank voltage in-phase with the first oscillating drive voltage, andgenerating, responsive to the first oscillating tank voltage, the firstoscillating drive voltage in-phase with the first oscillating tankvoltage. The first preferred embodiment enables a single-endedoscillating signal to be generated in a low complexity manner.

In a variant of the first preferred embodiment of the oscillatorcircuit, the first tank circuit may be arranged to generate, responsiveto the first oscillating drive voltage, the first oscillating tankvoltage one hundred and eighty degrees out-of-phase with the firstoscillating drive voltage, and the feedback stage may comprise a firstdriver arranged to generate, responsive to the first oscillating tankvoltage, the first oscillating drive voltage one hundred and eightydegrees out-of-phase with the first oscillating tank voltage by applyingsignal inversion to the first oscillating tank voltage. Likewise, avariant of the first preferred embodiment of the method may comprisegenerating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage one hundred and eighty degrees out-of-phasewith the first oscillating drive voltage, and generating, responsive tothe first oscillating tank voltage, the first oscillating drive voltageone hundred and eighty degrees out-of-phase with the first oscillatingtank voltage by applying signal inversion to the first oscillating tankvoltage. This variant enables a single-ended oscillating signal to begenerated in a low complexity manner.

In a second preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage in-phasewith the first oscillating drive voltage, and the feedback stage maycomprise:

a second driver arranged to generate a second oscillating drive voltageby applying signal inversion to the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage in-phasewith the second oscillating drive voltage; and

a first driver arranged to generate the first oscillating drive voltageby applying signal inversion to the second oscillating tank voltage.

Likewise, a second preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage in-phase with the first oscillating drivevoltage,

generating a second oscillating drive voltage by applying signalinversion to the first oscillating tank voltage;

generate, responsive to the second oscillating drive voltage, a secondoscillating tank voltage in-phase with the second oscillating drivevoltage; and

generating the first oscillating drive voltage by applying signalinversion to the second oscillating tank voltage.

The second preferred embodiment enables a balanced oscillating signal tobe generated in a low complexity manner. The use of first and secondtank circuits enables an accurate phase difference to be provided in alow complexity manner.

In a first variant of the second preferred embodiment of the oscillatorcircuit, the first tank circuit may be arranged to generate, responsiveto the first oscillating drive voltage, the first oscillating tankvoltage one hundred and eighty degrees out-of-phase +with the firstoscillating drive voltage, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltageby applying signal inversion to the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage in-phasewith the second oscillating drive voltage; and

a first driver arranged to generate the first oscillating drive voltagein-phase with the second oscillating tank voltage.

Likewise, a first variant of the second preferred embodiment of themethod may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage one hundred and eighty degrees out-of-phasewith the first oscillating drive voltage;

generating a second oscillating drive voltage by applying signalinversion to the first oscillating tank voltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage in-phase with the second oscillating drivevoltage; and

generating the first oscillating drive voltage in-phase with the secondoscillating tank voltage.

This first variant enables a balanced oscillating signal to be generatedin a low complexity manner, and an accurate phase difference to beprovided with low complexity.

In a second variant of the second preferred embodiment of the oscillatorcircuit, the first tank circuit may be arranged to generate, responsiveto the first oscillating drive voltage, the first oscillating tankvoltage one hundred and eighty degrees out-of-phase with the firstoscillating drive voltage, and the feedback stage may comprise:

a second driver arranged to generate, responsive to the firstoscillating tank voltage, a second oscillating drive voltage in-phasewith the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage one hundredand eighty degrees out-of-phase with the second oscillating drivevoltage; and

a first driver arranged to generate, responsive to the secondoscillating tank voltage, the first oscillating drive voltage in-phasewith the second oscillating tank voltage.

Likewise, a second variant of the second preferred embodiment of themethod may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage one hundred and eighty degrees out-of-phasewith the first oscillating drive voltage;

generating, responsive to the first oscillating tank voltage, a secondoscillating drive voltage in-phase with the first oscillating tankvoltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage one hundred and eighty degrees out-of-phasewith the second oscillating drive voltage; and

generating, responsive to the second oscillating tank voltage, the firstoscillating drive voltage in-phase with the second oscillating tankvoltage.

This second variant enables a balanced oscillating signal to begenerated in a low complexity manner, and an accurate phase differenceto be provided with low complexity.

In the first and second preferred embodiments of the oscillator circuit,and their variants, the first tank circuit may comprise a sensor devicearranged to generate the first oscillating tank voltage responsive tothe first oscillating tank current. Likewise, the first and secondpreferred embodiments of the method, and their variants, may comprisegenerating in a sensor device the first oscillating tank voltageresponsive to the first oscillating tank current. The sensor device maycomprise one of a resistive element and a transformer coupled in serieswith the first inductive element and the first capacitive elementbetween the voltage rail and the first drive node. Alternatively, thesensor device may be magnetically coupled to the first inductive elementfor generating by magnetic induction the first oscillating tank voltageresponsive to the first oscillating tank current. These features enablefeedback to be provided in a low complexity manner.

In a third preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise a phase shifting stagearranged to generate a first intermediate oscillating voltage byapplying a phase lag of ninety degrees to the first oscillating tankvoltage, and a first driver arranged to generate the first oscillatingdrive voltage by applying signal inversion to the first intermediateoscillating voltage.

Likewise, a third preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase lagging by ninety degrees aphase of the first oscillating drive voltage;

generating a first intermediate oscillating voltage by applying a phaselag of ninety degrees to the first oscillating tank voltage; and

generating the first oscillating drive voltage by applying signalinversion to the first intermediate oscillating voltage.

The third preferred embodiment enables quadrature-related signals to begenerated in a low complexity manner.

In a fourth preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase leading by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise a phase shifting stagearranged to generate a first intermediate oscillating voltage byapplying a phase lag of ninety degrees to the first oscillating tankvoltage, and a first driver arranged to generate the first oscillatingdrive voltage in response to, and in-phase with, the first intermediateoscillating voltage.

Likewise, a fourth preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase leading by ninety degrees aphase of the first oscillating drive voltage;

generating a first intermediate oscillating voltage by applying a phaselag of ninety degrees to the first oscillating tank voltage; and

generating the first oscillating drive voltage in response to, andin-phase with, the first intermediate oscillating voltage.

The fourth preferred embodiment enables quadrature-related signals to begenerated in a low complexity manner.

In a fifth preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a first phase shift circuit arranged to generate a first intermediateoscillating voltage by applying a phase lag of ninety degrees to thefirst oscillating tank voltage;

a second driver arranged to generate, responsive to the firstintermediate oscillating voltage, a second oscillating drive voltagein-phase with the first intermediate oscillating voltage,

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase lagging by ninety degrees a phase of a second oscillating drivevoltage;

a second phase shift circuit arranged to generate a second intermediateoscillating voltage by applying a phase lag of ninety degrees to thesecond oscillating tank voltage; and

a first driver arranged to generate, responsive to the secondintermediate oscillating voltage, the first oscillating drive voltagein-phase with the second intermediate oscillating voltage.

Likewise, a fifth preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase lagging by ninety degrees aphase of the first oscillating drive voltage;

generating a first intermediate oscillating voltage by applying a phaselag of ninety degrees to the first oscillating tank voltage;

generating, responsive to the first intermediate oscillating voltage, asecond oscillating drive voltage in-phase with the first intermediateoscillating voltage,

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage having a phase lagging by ninety degrees aphase of a second oscillating drive voltage;

generating a second intermediate oscillating voltage by applying a phaselag of ninety degrees to the second oscillating tank voltage; and

generating, responsive to the second intermediate oscillating voltage,the first oscillating drive voltage in-phase with the secondintermediate oscillating voltage.

The fifth preferred embodiment enables a balanced oscillating signal tobe generated in a low complexity manner.

In a sixth preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a first phase shift circuit arranged to generate a first intermediateoscillating voltage by applying a phase lag of ninety degrees to thefirst oscillating tank voltage;

a second driver arranged to generate a second oscillating drive voltageby applying signal inversion to the first intermediate oscillatingvoltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase leading by ninety degrees a phase of the second oscillating drivevoltage;

a second phase shift circuit arranged to generate a second intermediateoscillating voltage by applying a phase lag of ninety degrees to thesecond oscillating tank voltage; and

a first driver arranged to generate, responsive to the secondintermediate oscillating voltage, the first oscillating drive voltagein-phase with the second intermediate oscillating voltage.

Likewise, a sixth preferred embodiment of the method may comprise:

generate, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase lagging by ninety degrees aphase of the first oscillating drive voltage, and the feedback stage maycomprise:

a first phase shifter arranged to generate a first intermediateoscillating voltage by applying a phase lag of ninety degrees to thefirst oscillating tank voltage;

a second driver arranged to generate a second oscillating drive voltageby applying signal inversion to the first intermediate oscillatingvoltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase leading by ninety degrees a phase of the second oscillating drivevoltage;

a second phase shifter arranged to generate a second intermediateoscillating voltage by applying a phase lag of ninety degrees to thesecond oscillating tank voltage; and

a first driver arranged to generate, responsive to the secondintermediate oscillating voltage, the first oscillating drive voltagein-phase with the second intermediate oscillating voltage.

The sixth preferred embodiment enables a balanced oscillating signal tobe generated in a low complexity manner.

In a seventh preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltageby applying signal inversion to the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase lagging by ninety degrees a phase of the second oscillating drivevoltage; and

a first driver arranged to generate, responsive to the secondoscillating tank voltage, the first oscillating drive voltage in-phasewith the second oscillating tank voltage.

Likewise, a seventh preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase lagging by ninety degrees aphase of the first oscillating drive voltage;

generating a second oscillating drive voltage by applying signalinversion to the first oscillating tank voltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage having a phase lagging by ninety degrees aphase of the second oscillating drive voltage; and

generating, responsive to the second oscillating tank voltage, the firstoscillating drive voltage in-phase with the second oscillating tankvoltage.

The seventh preferred embodiment enables a balanced oscillating signalto be generated in a low complexity manner.

In an eighth preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase leading by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltageby applying signal inversion to the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase leading by ninety degrees a phase of the second oscillating drivevoltage; and

a first driver arranged to generate, responsive to the secondoscillating tank voltage, the first oscillating drive voltage in-phasewith the second oscillating tank voltage.

Likewise, an eighth preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase leading by ninety degrees aphase of the first oscillating drive voltage;

generating a second oscillating drive voltage by applying signalinversion to the first oscillating tank voltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage having a phase leading by ninety degrees aphase of the second oscillating drive voltage; and

generating, responsive to the second oscillating tank voltage, the firstoscillating drive voltage in-phase with the second oscillating tankvoltage.

The eighth preferred embodiment enables quadrature-related signals to begenerated in a low complexity manner.

In a ninth preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase leading by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a second driver arranged to generate, responsive to the firstoscillating tank voltage, a second oscillating drive voltage in-phasewith the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase lagging by ninety degrees a phase of the second oscillating drivevoltage; and

a first driver arranged to generate, responsive to the secondoscillating tank voltage, the first oscillating drive voltage in-phasewith the second oscillating tank voltage.

Likewise, a ninth preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase leading by ninety degrees aphase of the first oscillating drive voltage;

generating, responsive to the first oscillating tank voltage, a secondoscillating drive voltage in-phase with the first oscillating tankvoltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage having a phase lagging by ninety degrees aphase of the second oscillating drive voltage; and

generating, responsive to the second oscillating tank voltage, the firstoscillating drive voltage in-phase with the second oscillating tankvoltage.

The ninth preferred embodiment enables quadrature-related oscillatingsignals to be generated in a low complexity manner.

In a tenth preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a second driver arranged to generate, responsive to the firstoscillating tank voltage, a second oscillating drive voltage in-phasewith the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase lagging by ninety degrees a phase of the second oscillating drivevoltage;

a third driver arranged to generate, responsive to the secondoscillating tank voltage, a third oscillating drive voltage in-phasewith the second oscillating tank voltage;

a third tank circuit arranged to generate, responsive to the thirdoscillating drive voltage, a third oscillating tank voltage having aphase lagging by ninety degrees a phase of the third oscillating drivevoltage;

a fourth driver arranged to generate, responsive to the thirdoscillating tank voltage, a fourth oscillating drive voltage in-phasewith the third oscillating tank voltage;

a fourth tank circuit arranged to generate, responsive to the fourthoscillating drive voltage, a fourth oscillating tank voltage having aphase lagging by ninety degrees a phase of the fourth oscillating drivevoltage; and

a first driver arranged to generate, responsive to the fourthoscillating tank voltage, the first oscillating drive voltage in-phasewith the fourth oscillating tank voltage.

Likewise, a tenth preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase lagging by ninety degrees aphase of the first oscillating drive voltage;

generating, responsive to the first oscillating tank voltage, a secondoscillating drive voltage in-phase with the first oscillating tankvoltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage having a phase lagging by ninety degrees aphase of the second oscillating drive voltage;

generating, responsive to the second oscillating tank voltage, a thirdoscillating drive voltage in-phase with the second oscillating tankvoltage;

generating, responsive to the third oscillating drive voltage, a thirdoscillating tank voltage having a phase lagging by ninety degrees aphase of the third oscillating drive voltage;

generating, responsive to the third oscillating tank voltage, a fourthoscillating drive voltage in-phase with the third oscillating tankvoltage;

generating, responsive to the fourth oscillating drive voltage, a fourthoscillating tank voltage having a phase lagging by ninety degrees aphase of the fourth oscillating drive voltage; and

generating, responsive to the fourth oscillating tank voltage, the firstoscillating drive voltage in-phase with the fourth oscillating tankvoltage.

The tenth preferred embodiment enables quadrature-related balancedoscillating signals to be generated in a low complexity manner.

In an eleventh preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase leading by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a second driver arranged to generate, responsive to the firstoscillating tank voltage, a second oscillating drive voltage in-phasewith the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase leading by ninety degrees a phase of the second oscillating drivevoltage;

a third driver arranged to generate, responsive to the secondoscillating tank voltage, a third oscillating drive voltage in-phasewith the second oscillating tank voltage;

a third tank circuit arranged to generate, responsive to the thirdoscillating drive voltage, a third oscillating tank voltage having aphase leading by ninety degrees a phase of the third oscillating drivevoltage;

a fourth driver arranged to generate, responsive to the thirdoscillating tank voltage, a fourth oscillating drive voltage in-phasewith the third oscillating tank voltage;

a fourth tank circuit arranged to generate, responsive to the fourthoscillating drive voltage, a fourth oscillating tank voltage having aphase leading by ninety degrees a phase of the fourth oscillating drivevoltage; and

a first driver arranged to generate, responsive to the fourthoscillating tank voltage, the first oscillating drive voltage in-phasewith the fourth oscillating tank voltage.

Likewise, an eleventh preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase leading by ninety degrees aphase of the first oscillating drive voltage;

generating, responsive to the first oscillating tank voltage, a secondoscillating drive voltage in-phase with the first oscillating tankvoltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage having a phase leading by ninety degrees aphase of the second oscillating drive voltage;

generating, responsive to the second oscillating tank voltage, a thirdoscillating drive voltage in-phase with the second oscillating tankvoltage;

generating, responsive to the third oscillating drive voltage, a thirdoscillating tank voltage having a phase leading by ninety degrees aphase of the third oscillating drive voltage;

generating, responsive to the third oscillating tank voltage, a fourthoscillating drive voltage in-phase with the third oscillating tankvoltage;

generating, responsive to the fourth oscillating drive voltage, a fourthoscillating tank voltage having a phase leading by ninety degrees aphase of the fourth oscillating drive voltage; and

generating, responsive to the fourth oscillating tank voltage, the firstoscillating drive voltage in-phase with the fourth oscillating tankvoltage.

The eleventh preferred embodiment enables quadrature-related balancedoscillating signals to be generated in a low complexity manner.

In the tenth and eleventh preferred embodiment of the oscillatorcircuit, the first driver may comprise:

a first transistor having a drain coupled to a first power supply rail,a source coupled to an output of the first driver, and a gate coupled toan input of the first driver by a first coupling capacitor, and a secondtransistor having a drain coupled to the output of the first driver, asource coupled to a second power supply rail, and a gate coupled to thefirst power supply rail by a first resistor;

and the third driver may comprise:

a third transistor having a drain coupled to the first power supplyrail, a source coupled to an output of the third driver, and a gatecoupled to an input of the third driver by a second coupling capacitor,and a fourth transistor having a drain coupled to the output of thethird driver, and a source coupled to the first power supply rail by asecond resistor;

wherein the gate of the first transistor is coupled to a gate of thefourth transistor, and the gate of the third transistor is coupled tothe gate of the second transistor; andwherein the first, second, third and fourth transistors are n-channelcomplementary metal oxide silicon, CMOS, transistors.

The use of n-channel CMOS transistors, rather than p-channel CMOStransistors, for coupling the first and third tank circuits to the thirdpower supply rail enables the transistors to be implemented with lessintegrated circuit chip area and less parasitic capacitance.

In a twelfth preferred embodiment of the oscillator circuit, the firsttank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltageby applying signal inversion to the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase lagging by ninety degrees a phase of the second oscillating drivevoltage;

a third driver arranged to generate a third oscillating drive voltage byapplying signal inversion to the second oscillating tank voltage;

a third tank circuit arranged to generate, responsive to the thirdoscillating drive voltage, a third oscillating tank voltage having aphase lagging by ninety degrees a phase of the third oscillating drivevoltage;

a fourth driver arranged to generate a fourth oscillating drive voltageby applying signal inversion to the third oscillating tank voltage;

a fourth tank circuit arranged to generate, responsive to the fourthoscillating drive voltage, a fourth oscillating tank voltage having aphase lagging by ninety degrees a phase of the fourth oscillating drivevoltage; and

a first driver arranged to generate the first oscillating drive voltageby applying signal inversion to the fourth oscillating tank voltage.

Likewise, a twelfth preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase lagging by ninety degrees aphase of the first oscillating drive voltage;

generating a second oscillating drive voltage by applying signalinversion to the first oscillating tank voltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage having a phase lagging by ninety degrees aphase of the second oscillating drive voltage;

generating a third oscillating drive voltage by applying signalinversion to the second oscillating tank voltage;

generating, responsive to the third oscillating drive voltage, a thirdoscillating tank voltage having a phase lagging by ninety degrees aphase of the third oscillating drive voltage;

generating a fourth oscillating drive voltage by applying signalinversion to the third oscillating tank voltage;

generating, responsive to the fourth oscillating drive voltage, a fourthoscillating tank voltage having a phase lagging by ninety degrees aphase of the fourth oscillating drive voltage; and

generating the first oscillating drive voltage by applying signalinversion to the fourth oscillating tank voltage.

The twelfth preferred embodiment enables quadrature-related balancedoscillating signals to be generated in a low complexity manner.

In a thirteenth preferred embodiment of the oscillator circuit, thefirst tank circuit may be arranged to generate, responsive to the firstoscillating drive voltage, the first oscillating tank voltage having aphase leading by ninety degrees a phase of the first oscillating drivevoltage, and the feedback stage may comprise:

a second driver arranged to generate a second oscillating drive voltageby applying signal inversion to the first oscillating tank voltage;

a second tank circuit arranged to generate, responsive to the secondoscillating drive voltage, a second oscillating tank voltage having aphase leading by ninety degrees a phase of the second oscillating drivevoltage;

a third driver arranged to generate a third oscillating drive voltage byapplying signal inversion to the second oscillating tank voltage;

a third tank circuit arranged to generate, responsive to the thirdoscillating drive voltage, a third oscillating tank voltage having aphase leading by ninety degrees a phase of the third oscillating drivevoltage;

a fourth driver arranged to generate a fourth oscillating drive voltageby applying signal inversion to the third oscillating tank voltage;

a fourth tank circuit arranged to generate, responsive to the fourthoscillating drive voltage, a fourth oscillating tank voltage having aphase leading by ninety degrees a phase of the fourth oscillating drivevoltage; and

a first driver arranged to generate the first oscillating drive voltageby applying signal inversion to the fourth oscillating tank voltage.

Likewise, a thirteenth preferred embodiment of the method may comprise:

generating, responsive to the first oscillating drive voltage, the firstoscillating tank voltage having a phase leading by ninety degrees aphase of the first oscillating drive voltage;

generating a second oscillating drive voltage by applying signalinversion to the first oscillating tank voltage;

generating, responsive to the second oscillating drive voltage, a secondoscillating tank voltage having a phase leading by ninety degrees aphase of the second oscillating drive voltage;

generating a third oscillating drive voltage by applying signalinversion to the second oscillating tank voltage;

generating, responsive to the third oscillating drive voltage, a thirdoscillating tank voltage having a phase leading by ninety degrees aphase of the third oscillating drive voltage;

generating a fourth oscillating drive voltage by applying signalinversion to the third oscillating tank voltage;

generating, responsive to the fourth oscillating drive voltage, a fourthoscillating tank voltage having a phase leading by ninety degrees aphase of the fourth oscillating drive voltage; and

generating the first oscillating drive voltage by applying signalinversion to the fourth oscillating tank voltage.

The thirteenth preferred embodiment enables quadrature-related balancedoscillating signals to be generated in a low complexity manner.

In the third, fifth, sixth, seventh, tenth and twelfth preferredembodiments of the oscillator circuit, the capacitive element may becoupled between the first drive node and the first tank output and theinductive element may be coupled between the first tank output and thefirst voltage rail.

In the first, second, fourth, eighth, ninth, eleventh and thirteenthpreferred embodiments of the oscillator circuit, the inductive elementmay be coupled between the first drive node and the first tank outputand the capacitive element may be coupled between the first tank outputand the first voltage rail.

The third to ninth preferred embodiments may comprise a variablecapacitance element coupled between the first tank output and the secondtank output. This feature enables a frequency of oscillation to bevaried.

In the tenth and eleventh preferred embodiments, the second driver maycomprise: a fifth transistor having a drain coupled to a third powersupply rail, a source coupled to an output of the second driver, and agate coupled to an input of the second driver by a third couplingcapacitor; and

a sixth transistor having a drain coupled to the output of the seconddriver, a source coupled to a fourth power supply rail, and a gatecoupled to the third power supply rail by a third resistor;

the fourth driver may comprise:

a seventh transistor having a drain coupled to the third power supplyrail, a source coupled to an output of the fourth driver, and a gatecoupled to an input of the fourth driver by a fourth coupling capacitorand

an eighth transistor having a drain coupled to the output of the fourthdriver, a source coupled to the fourth power supply rail, and a gatecoupled to the third power supply rail by a fourth resistor;

wherein the gate of the fifth transistor may be coupled to the gate ofthe eighth transistor, and the gate of the seventh transistor may becoupled to the gate of the sixth transistor; and

wherein the fifth, sixth, seventh and eighth transistors may ben-channel CMOS transistors.

The use of n-channel CMOS transistors, rather than p-channel CMOStransistors, for coupling the second and fourth tank circuits to thethird power supply rail, and for coupling the fifth and seventhtransistors to the fifth power supply rail, enables the transistors tobe implemented with less integrated circuit chip area and less parasiticcapacitance.

In the second and fifth to ninth preferred embodiments of the oscillatorcircuit, and their variants, the first tank circuit and the second tankcircuit may have an equal resonance frequency. In the tenth tothirteenth preferred embodiments of the oscillator circuits, the first,second, third and fourth tank circuits may have an equal resonancefrequency. These features enable high power efficiency.

In the second and fifth to ninth preferred embodiments of the oscillatorcircuit, and their variants, the first tank circuit and the second tankcircuit may have an equal capacitance and an equal inductance. In thetenth to thirteenth preferred embodiments of the oscillator circuits,the first, second, third and fourth tank circuits may have an equalcapacitance and an equal inductance. These features enable closematching of resonance frequencies.

There is also provided a wireless communication device comprising anoscillator circuit according to the first aspect.

Preferred embodiments are described, by way of example only, withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a prior art oscillator.

FIG. 2 is a schematic diagram illustrating the principle of operation ofan oscillator employing voltage driven series resonance.

FIG. 3 is a schematic diagram of an oscillator circuit.

FIGS. 4 to 8 are schematic diagrams illustrating different tankconfigurations of a tank circuit.

FIGS. 9 to 18 are schematic diagrams of oscillator circuits.

FIG. 19 is a schematic diagram of drivers.

FIG. 20 is a schematic diagram of an oscillator circuit having provisionfor tuning.

FIG. 21 is a graph of phase noise as a function of frequency for theoscillator circuit described with reference to FIG. 18.

FIG. 22 is a schematic diagram of a wireless communication apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, an oscillator topology is disclosed thatemploys series resonance between an inductor and a capacitor, ratherthan the parallel resonance of conventional oscillators, and in whichthe tank formed by the inductor and capacitor is voltage driven. Theprinciple of operation of an oscillator circuit employing voltagedriven, or voltage-mode, series resonance is described with reference toFIG. 2. Referring to FIG. 2, an inductor, or inductive element, L and acapacitor, or capacitive element, C are coupled in series, and therebyconstitute a tank circuit T, or resonator. The inductive element L iscoupled between a voltage rail at ground potential, and a junction 1,and the capacitive element C is coupled between the junction 1 and adrive node 2. Therefore, the inductive element L and the capacitive Care coupled together at the junction 1. If a sinusoidal drive, orexcitation, voltage V_(D)=V_(dd)·sin(ωt), where V_(dd) is a voltagesupplied by a power supply node 5, ω is the resonance frequency inradians per second of the series coupled inductive element L andcapacitive element C, and t is time, is applied at the drive node 2 by avoltage generator G, a tank voltage V_(T)=Q·V_(dd)·sin(wt−π/2), where Qis the quality factor of the series coupled inductive element L andcapacitive element C, is generated at the junction 1. Therefore, theamplitude of the tank voltage V_(T) is Q times the amplitude of thedrive voltage V_(D), and is shifted, that is, delayed, in phase by π/2radians, that is, 90°, relative to the drive voltage V_(D). Typically,for present-day integrated circuit processes, the quality factor Q canbe ten, and therefore the tank voltage V_(T) can be high when the drivevoltage V_(D) is small. It is not essential for the drive voltage V_(D)to be sinusoidal, and alternatively it may have, for example, a squareor rectangular waveform, or an approximately square or rectangularwaveform having finite rise and fall times.

For the voltage-mode series resonance oscillator illustrated in FIG. 2,the amplitude of the tank voltage V_(T), can be expressed as

k·ωL·V _(dd) /R _(SEQ) =k·Q·V _(BIAS)  (2)

where ωL is the impedance of the inductive element L at the resonancefrequency ω, V_(dd) is the amplitude, determined by the power supplynode 5, of the drive voltage V_(D) driving the series resonance, R_(SEQ)is the equivalent series tank resistance, Q is the quality factor of thetank comprising the inductive element L and the capacitive element C,and k is a proportionality factor.

A comparison between equations (1) and (2) reveals significantdifferences between the voltage-mode series resonance oscillator and acurrent-mode parallel resonance oscillator. In the current-mode parallelresonance oscillator, the oscillation amplitude is proportional to thebias current I_(BIAS), and if the tank quality factor Q is high, thatis, if the parallel tank resistance is high, the bias current I_(BIAS)is low. Furthermore, the power supply voltage of the current-modeparallel resonance oscillator limits the maximum oscillation amplitude.In the voltage-mode series resonance oscillator, if the tank qualityfactor Q is high, that is, the series tank resistance is low, thecurrent drawn from a power supply is high, and the oscillation amplitudeis also high, the tank quality factor Q being inversely proportional tothe series tank resistance. Furthermore, in the voltage-mode seriesresonance oscillator, no straightforward limitation to the amplitude ofthe oscillation is imposed by the value of the power supply voltageV_(dd), which enables a very high oscillation amplitude in the presenceof a very low power supply voltage, if the tank quality factor Q issufficiently high. This can enable a very low phase noise of theoscillator, albeit with a large current from the power supply.

Continuing with reference to FIG. 2, the drive voltage V_(D) and thetank voltage V_(T) have a quadrature phase relationship, or, expressedmore concisely, are in quadrature. In particular, the phase of the drivevoltage V_(D) leads the phase of the tank voltage V_(T) by 90°. In otherwords, the phase of the drive voltage V_(D) lags the phase of the tankvoltage V_(T) by 90°. However, alternative configurations of the tankmay be used, as described below, in which different phase relationshipsapply between the drive voltage V_(D) and the tank voltage V_(T). In apractical embodiment of an oscillator circuit employing the seriesresonance of a tank, the oscillator circuit itself can provide the drivevoltage V_(D). For example, the drive voltage V_(D) can be generatedfrom the tank voltage V_(T), or generated by switching on and off thepower supply voltage V_(dd). Where the drive voltage V_(D) is generatedfrom the tank voltage V_(T), it is necessary to ensure the requiredphase relationship between the tank voltage V_(T) and the drive voltageV_(D) for providing positive feedback to sustain oscillation.

Referring to FIG. 3, an oscillator circuit 100 comprises a first tankcircuit T1 and a feedback (FB) stage F. The first tank circuit T1 has afirst drive node 12 at which a first oscillating drive voltage V_(D1) isapplied to the first tank circuit T1, and a first tank output 13 atwhich the first oscillating tank voltage V_(T1) is delivered from thefirst tank circuit T1. The first tank circuit T1 of FIG. 3 may have oneof several alternative tank configurations, which are described below,of an inductive element L and a capacitive element C coupled in seriesbetween the first drive node 12 and a voltage rail 14. The feedbackstage F has an input 17 coupled to the first tank output 13 forreceiving the first oscillating tank voltage V_(T1), and an output 18coupled to the first drive node 12 for delivering the first oscillatingdrive voltage V_(D1) to the first drive node 12. The feedback stage Fhas one of several different feedback configurations as described below,and is arranged to generate, responsive to the first oscillating tankvoltage V_(T1), the first oscillating drive voltage V_(D1) in-phase withan oscillating tank current I_(T) flowing in the inductive element L andthe capacitive element C between the first drive node 12 and the voltagerail 14, thereby causing the oscillator circuit 100 to oscillate in aseries resonance mode of the inductive element L and the capacitiveelement C.

Tank configurations of the first tank circuit T1 are described withreference to FIGS. 4 to 8. In each of these tank configurations, thecapacitive element C and the inductive element L are coupled in seriesbetween the first drive node 12 and the voltage rail 14, which may be atground potential or another potential.

Referring to FIG. 4, a first tank configuration of the first tankcircuit T1 has the capacitive element C coupled between the first drivenode 12 and a junction 11, and the inductive element L coupled betweenthe junction 11 and the voltage rail 14. This first tank configuration,therefore, corresponds to the configuration of the tank circuit Tillustrated in FIG. 2. The junction 11 is coupled to the first tankoutput 13. In this first tank configuration, the first oscillating tankvoltage V_(T1) present at the first tank output 13 has a phase that lagsa phase of the first oscillating drive voltage V_(D1) by 90°.

Referring to FIG. 5, a second tank configuration of the first tankcircuit T1 has the inductive element L coupled between the first drivenode 12 and the junction 11, and the capacitive element C coupledbetween the junction 11 and the voltage rail 14. The junction 11 iscoupled to the first tank output 13. This second tank configuration,therefore, corresponds to the first tank configuration illustrated inFIG. 4, but with the position of the inductive element L and thecapacitive element C swapped. In this second tank configuration, thefirst oscillating tank voltage V_(T1) has a phase that leads a phase ofthe first oscillating drive voltage V_(D1) by 90°.

Referring to FIG. 6, a third tank configuration of the first tankcircuit T1 has a sensor device S coupled in series with the inductiveelement L and the capacitive element C between the first drive node 12and the voltage rail 14. In particular, the sensor device S is coupledbetween the inductive element L and the capacitive element C, althoughin non-illustrated variants of the third tank configuration, the sensordevice S may instead be coupled between the first drive node 12 and thecapacitive element C, or between the inductive element L and the voltagerail 14. In further non-illustrated variants of the third tankconfiguration, the position of the inductive element L and thecapacitive element C may be swapped, such that the sensor device S iscoupled between the inductive element L and the capacitive element C,with the capacitive element C coupled between the voltage rail 14 andthe sensor device S, and the inductive element L coupled between thefirst drive node 12 and the sensor device S, or the sensor device Sinstead be coupled between the first drive node 12 and the inductiveelement L, or the sensor device S instead coupled between the voltagerail 14 and the capacitive element C. The oscillating tank current I_(T)flows in response to the first oscillating drive voltage V_(D1), and thesensor device S is arranged to generate the first oscillating tankvoltage V_(T1) responsive to the oscillating tank current I_(T). Inparticular, in the third tank configuration illustrated in FIG. 6, thesensor device S comprises a resistive element R, and the first tankoutput 13 comprises a pair of terminals 13 a, 13 b coupled to differentterminals of the resistive element R. The oscillating tank current I_(T)flows through the resistive element R, thereby giving rise to the firstoscillating tank voltage V_(T1) across the resistive element R, andhence between the pair of terminals 13 a, 13 b. In those variants of thethird tank configuration in which one of the terminals of the resistiveelement R is coupled directly to the voltage rail 14, rather than viathe inductive element L or via the capacitive element C, the first tankoutput 13 may instead be coupled to only the other terminal of theresistive element R, that is not coupled directly to the voltage rail14. The oscillating tank current I_(T) is in-phase with the firstoscillating drive voltage V_(D1), and the first oscillating tank voltageV_(T1) is in-phase with the oscillating tank current I_(T), andtherefore is in-phase with the first oscillating drive voltage V_(D1).

Referring to FIG. 7, a fourth tank configuration of the first tankcircuit T1 has a sensor device S coupled in series with the inductiveelement L and the capacitive element C between the first drive node 12and the voltage rail 14. In particular, the sensor device S is coupledbetween the inductive element L and the capacitive element C, althoughthe alternative positions of the sensor device S described above withreference to FIG. 6 are also applicable to the sensor device Sillustrated in the tank configuration of FIG. 7. The oscillating tankcurrent I_(T) flows in response to the first oscillating drive voltageV_(D1), and the sensor device S illustrated in FIG. 7 is arranged togenerate the first oscillating tank voltage V_(T1) responsive to theoscillating tank current I_(T). In particular, in the fourth tankconfiguration illustrated in FIG. 7, the sensor device S comprises atransformer X having a primary winding X_(P) coupled in series with theinductive element L and the capacitive element C between the first drivenode 12 and the voltage rail 14, a secondary winding X_(S) coupled to apair of terminals 13 a, 13 b of the first tank output 13, and aresistive element R coupled between the pair of terminals 13 a, 13 b inparallel with the secondary winding X_(S). The resistive element R has asmaller resistance, for example one tenth or less, than the impedance ofthe secondary winding X_(S) at the frequency of oscillation. Theoscillating tank current I_(T) flows through the primary winding X_(P),thereby giving rise to an oscillating sensor current flowing in thesecondary winding X_(S). The oscillating sensor current flows in thesecondary winding X_(S) and the resistive element R, and hence givesrise to the first oscillating tank voltage V_(T1) between the pair ofterminals 13 a, 13 b. Optionally, one terminal of the pair of terminals13 a, 13 b may be coupled to the voltage rail 14, or to another voltagerail, in which case the first tank output 13 may instead comprise asingle one of the terminals of the pair of terminals 13 a, 13 b. Theoscillating tank current I_(T) is in-phase with the first oscillatingdrive voltage V_(D1), and consequently the oscillating sensor currentflowing in the secondary winding X_(S) and the resistive element R isin-phase with the oscillating tank current I_(T) and the firstoscillating drive voltage V_(D1). Flow of the oscillating sensor currentin the resistive element R gives rise to the first oscillating tankvoltage V_(T1) in-phase with the oscillating sensor current. Therefore,the first oscillating tank voltage V_(T1) at the first tank output 13 isin-phase with the oscillating tank current I_(T), and therefore isin-phase with the first oscillating drive voltage V_(D1). In a variationof the fourth tank configuration described with reference to FIG. 7, theresistive element R may be replaced by a trans-resistance amplifierhaving inputs coupled to respective terminals of the secondary windingX_(S), instead of the secondary winding X_(S) being coupled directly tothe pair of terminals 13 a, 13 b of the first tank output 13, and anoutput of the trans-resistance amplifier coupled to the first tankoutput 13, or the pair of terminals 13 a, 13 b of the first tank output13.

Referring to FIG. 8, a fifth tank configuration of the first tankcircuit T1 comprises the inductive element L and the capacitive elementC arranged as illustrated in FIG. 4, or alternatively they may bearranged as illustrated in FIG. 5. The first tank circuit T1 of FIG. 8further comprises a sensor device S magnetically coupled to theinductive element L. In particular, the inductive element L and a coil Mof the sensor device S are coupled magnetically thereby forming atransformer Y, with the inductive element L being a primary winding ofthe transformer Y and the coil M being a secondary winding of thetransformer Y. The coil M is coupled to a pair of terminals 13 a, 13 bof the first tank output 13, and a resistive element R is coupledbetween the pair of terminals 13 a, 13 b in parallel with the coil M.The resistive element R has a smaller resistance, for example one tenthor less, than the impedance of the coil M at the frequency ofoscillation. In response to the first oscillating drive voltage V_(D1),the oscillating tank current I_(T) flows through the inductive elementL, thereby giving rise to an oscillating sensor current flowing in thecoil M. The oscillating sensor current flows in the coil M and theresistive element R, and hence gives rise to the first oscillating tankvoltage V_(T1) between the pair of terminals 13 a, 13 b. Therefore, thesensor device S of FIG. 8 is arranged to generate the first oscillatingtank voltage V_(T1) responsive to the oscillating tank current I_(T) bymagnetic induction. Optionally, one terminal of the pair of terminals 13a, 13 b may be coupled to the voltage rail 14, or to another voltagerail, in which case the first tank output 13 may instead comprise asingle one of the terminals of the pair of terminals 13 a, 13 b. Theoscillating tank current I_(T) is in-phase with the first oscillatingdrive voltage V_(D1), and consequently the oscillating sensor currentflowing in the coil M and the resistive element R is in-phase with theoscillating tank current I_(T) and the first oscillating drive voltageV_(D1). Flow of the oscillating sensor current in the resistive elementR gives rise to the first oscillating tank voltage V_(T1) in-phase withthe oscillating sensor current. Therefore, the first oscillating tankvoltage V_(T1) at the first tank output 13 is in-phase with theoscillating tank current I_(T), and therefore is in-phase with the firstoscillating drive voltage V_(D1). In a variation of the fifth tankconfiguration described with reference to FIG. 8, the resistive elementR may be replaced by a trans-resistance amplifier having inputs coupledto respective terminals of the coil M, instead of the coil M beingcoupled directly to the pair of terminals 13 a, 13 b of the first tankoutput 13, and an output of the trans-resistance amplifier coupled tothe first tank output 13, or the pair of terminals 13 a, 13 b of thefirst tank output 13.

In a modified version of the third, fourth or fifth tank configurations,or their variants described above, connections of the sensor S to thepair of terminals 13 a, 13 b may be swapped, thereby inverting the firstoscillating tank voltage V_(T1), or, equivalently, modifying the phaseof the first oscillating tank voltage V_(T1) by 180°. In this case,although the oscillating tank current I_(T) is in-phase with the firstdrive voltage V_(D1), the first oscillating tank voltage V_(T1) is 180°out-of-phase with the oscillating tank current I_(T), and therefore is180° out-of-phase with the first oscillating drive voltage V_(D1).

Embodiments of the oscillator circuit 100 comprising the different tankconfigurations of the first tank circuit T1 described with reference toFIGS. 4 to 8, and having different feedback configurations of thefeedback stage F, are described below with reference to FIGS. 9 to 19.Some of these embodiments comprise a second tank circuit T2, in additionto the first tank circuit T1, and some of these embodiments furthercomprise a third tank circuit T3 and fourth tank circuit T4, in additionto the first and second tank circuits T1, T2. Such second, third andfourth tank circuits T2, T3, T4 may each have a tank configurationcorresponding to one of the first to fifth tank configurations describedwith reference to FIGS. 4 to 8, and therefore have respective second,third and fourth drive nodes referenced 22, 32, 42 at which respectivesecond, third and fourth oscillating drive voltages V_(D2), V_(D3),V_(D4) are applied, and respective second, third and fourth tank outputsreferenced 23, 33, 43 at which respective second, third and fourthoscillating tank voltages V_(T2), V_(T3), V_(T4) are delivered.

The particular tank configurations which each of the first, second,third and fourth tank circuits T1, T2, T3, T4 may have is dependent onwhether the respective tank circuit is required to generate therespective oscillating tank voltage in-phase with, or leading by a phaseof 90°, or lagging by a phase of 90°, or is 180° out-of-phase with, therespective first, second, third and fourth oscillating drive voltagesV_(D1), V_(D2), V_(D3), V_(D4). In particular, where the first, second,third or fourth tank circuit T1, T2, T3, T4 is required to generate therespective first, second, third or fourth oscillating tank voltageV_(T1), V_(T2), V_(T3), V_(T4) having a phase that lags by 90° a phaseof the respective first, second, third or fourth oscillating drivevoltage, the first, second, third or fourth tank circuit T1, T2, T3, T4may have the first tank configuration described with reference to FIG.4. Where the first, second, third or fourth tank circuit T1, T2, T3, T4is required to generate the respective first, second, third or fourthoscillating tank voltage V_(T1), V_(T2), V_(T3), V_(T4) having a phasethat leads by 90° a phase of the respective first, second, third orfourth oscillating drive voltage, the first, second, third or fourthtank circuit T1, T2, T3, T4 may have the second tank configurationdescribed with reference to FIG. 5. Where the first, second, third orfourth tank circuit T1, T2, T3, T4 is required to generate therespective first, second, third or fourth oscillating tank voltageV_(T1), V_(T2), V_(T3), V_(T4) in-phase with the respective first,second, third or fourth oscillating drive voltage V_(D1), V_(D2),V_(D3), V_(D4), the first, second, third or fourth tank circuit T1, T2,T3, T4 may have any of the third, fourth or fifth tank configuration, ortheir variants, described with reference to FIGS. 6, 7 and 8. Where thefirst, second, third or fourth tank circuit T1, T2, T3, T4 is requiredto generate the respective first, second, third or fourth oscillatingtank voltage V_(T1), V_(T2), V_(T3), V_(T4) 180° out-of-phase with therespective first, second, third or fourth oscillating drive voltageV_(D1), V_(D2), V_(D3), V_(D4), the first, second, third or fourth tankcircuit T1, T2, T3, T4 may have the modified version of any of thethird, fourth or fifth tank configurations, or their variants, describedwith reference to FIGS. 6, 7 and 8.

Although the first to fifth tank configurations described with referenceto FIGS. 4 to 8 have the same voltage rail 14, any or all of the first,second, third or fourth tank circuit T1, T2, T3, T4 may have differentvoltage rails providing different voltages.

Referring to FIG. 9, in a first preferred embodiment, an oscillatorcircuit 110 comprises the first tank circuit T1 and the feedback stage Fas described in relation to the oscillator circuit 100 of FIG. 3, thefeedback stage F having a first feedback configuration in which thefeedback stage F comprises a first driver D1 coupled in series betweenthe input 17 of the feedback stage F and the output 18 of the feedbackstage F. The first tank circuit T1 generates the first oscillating tankvoltage V_(T1) at the first tank output 13 in response to the firstoscillating drive voltage V_(D1) applied at the first drive node 12. Thefirst tank output 13 is coupled to the input 17 of the feedback stage F,and the first drive node 12 is coupled to the output 18 of the feedbackstage F. In the first preferred embodiment, the first tank circuit T1generates the first oscillating tank voltage V_(T1) in-phase with thefirst oscillating drive voltage V_(D1), and therefore may have any ofthe third, fourth or fifth tank configurations, or their variants,described above with reference to FIG. 6, 7 or 8. The first driver D1generates the first oscillating drive voltage V_(D1) in response to, andin-phase with, the first oscillating tank voltage V_(T1), so does notintroduce any phase change, which is signified by “0°” in the Figures.The first driver D1 may have positive and negative input terminals, inother words, a differential input, coupled to the pair of terminals 13a, 13 b of the first tank output 13.

In a variant of the oscillator circuit 110 described with reference toFIG. 9, the first tank circuit T1 generates the first oscillating tankvoltage V_(T1) 180° out-of-phase with the first oscillating drivevoltage V_(D1), and therefore may have any of the modified third, fourthor fifth tank configurations, or their variants, described above withreference to FIG. 6, 7 or 8, and the first driver D1 applies signalinversion to the first oscillating tank voltage V_(T1), therebyintroducing a phase change of 180°, such that the first oscillatingdrive voltage V_(D1) is 180° out-of-phase with the first oscillatingtank voltage V_(T1), as required to sustain oscillation.

In some applications, an oscillator circuit is required that generates adifferential or balanced oscillating signal, that is, generates a pairof signals where one signal, also referred to as a first signalcomponent, is the inverse of the other signal, or second signalcomponent.

Referring to FIG. 10, in a second embodiment, an oscillator circuit 115generates such a balanced oscillating signal, and comprises the firsttank circuit T1 and the feedback stage F as described in relation to theoscillator circuit 100 of FIG. 3, the feedback stage F having a secondfeedback configuration. In the second feedback configuration, thefeedback stage F comprises a second tank circuit T2 having a seconddrive node 22 for applying a second oscillating drive voltage V_(D2) tothe second tank circuit T2, and a second tank output 23 for delivering asecond oscillating tank voltage V_(T2) from the second tank circuit T2.The second tank output 23 is coupled to the output 18 of the feedbackstage F via a first driver D1, and the second drive node 22 is coupledto the input 17 of the feedback stage F via a second driver D2. Thefirst tank circuit T1 generates the first oscillating tank voltageV_(T1) at the first tank output 13 in response to, and in-phase with,the first oscillating drive voltage V_(D1) applied at the first drivenode 12. The second driver D2 generates the second oscillating drivevoltage V_(D2) 180° out-of-phase with the first oscillating tank voltageV_(T1) by applying signal inversion, or in other words inverting, thefirst oscillating tank voltage V_(T1). The second tank circuit T2generates a second oscillating tank voltage V_(T2) at the second tankoutput 23 in response to, and in-phase with, the second oscillatingdrive voltage V_(D2) applied at the second drive node 22. The firstdriver D1 generates the first oscillating drive voltage V_(D1) 180°out-of-phase with the second oscillating tank voltage V_(T2) by applyingsignal inversion the second oscillating tank voltage V_(T2). Therefore,the first oscillating drive voltage V_(D1) is generated in response to,and in-phase with, the first oscillating tank voltage V_(T1), asrequired to sustain oscillation. The second oscillating tank voltageV_(T2) is 180° out-of-phase with respect to the first oscillating tankvoltage V_(T1), and consequently the first and second oscillating tankvoltages V_(T1), V_(T2) are available to be used as first and secondssignal components of a balanced oscillating signal.

In a first variant of the oscillator circuit 115 described withreference to FIG. 10, the first tank circuit T1 generates the firstoscillating tank voltage V_(T1) 180° out-of-phase with the firstoscillating drive voltage V_(D1), and the second driver D2 does notapply signal inversion to the first oscillating tank voltage V_(T1),such that the first oscillating drive voltage V_(D1) is 180°out-of-phase with the first oscillating tank voltage V_(T1).

In a second variant of the oscillator circuit 115 described withreference to FIG. 10, the first tank circuit T1 generates the firstoscillating tank voltage V_(T1) 180° out-of-phase with the firstoscillating drive voltage V_(D1), the second driver D2 does not applysignal inversion to the first oscillating tank voltage V_(T1), wherebythe second oscillating drive voltage V_(D2) is in-phase with the firstoscillating tank voltage V_(T1), the second tank circuit T2 generatesthe second oscillating tank voltage V_(T2) 180° out-of-phase with thesecond oscillating drive voltage V_(D2), and the first driver does notapply signal inversion to the second oscillating tank voltage V_(T2),with the result that the first oscillating drive voltage V_(D1) is 180°out-of-phase with the first oscillating tank voltage V_(T1). Therefore,the second oscillating tank voltage V_(T2) is 180° out-of-phase withrespect to the first oscillating tank voltage V_(T1), and consequentlythe first and second oscillating tank voltages V_(T1), V_(T2) may beused as first and second signal components of a balanced oscillatingsignal.

In some applications, an oscillator circuit is required that generates apair of oscillating signals that have a quadrature relationship, thatis, differ in phase by 90°. Such an oscillator circuit has applicationin, for example, local oscillator signal generation in wirelesscommunication apparatus. For the oscillator circuit 115, and its firstand second variants, described with reference to FIG. 10, the phaserelationship of the first and second oscillating tank voltages V_(T1),V_(T2) has been described, as this phase relationship is relevant toensuring positive feedback to sustain oscillation, and also as theseoscillating voltages may be used by an external apparatus.Alternatively, external apparatus may employ oscillating voltagesgenerated at other locations in the respective first and second tankcircuits T1, T2, and such oscillating voltages may have a differentphase than that of the first and second oscillating tank voltagesV_(T1), V_(T2). For example, where the first and second tank circuitsT1, T2 have any of the tank configurations described with reference toFIGS. 6, 7 and 8, an external apparatus may employ an oscillatingvoltage generated at the following locations: in tank configuration ofFIGS. 6 and 7, a junction 15 between the capacitive element C and thesensor S, or a junction 19 between the inductive element L and thesensor S; in the tank configuration of FIG. 8, the junction 11 betweenthe capacitive element and the inductive element. Therefore, dependingon the choice of tank configurations and their variants, which need notbe the same for both the first and second tank circuits T1, T2, externalapparatus may employ oscillating voltages that lead or lag the first andsecond oscillating tank voltages V_(T1), V_(T2) by 90°, and, inparticular, oscillating voltages having a quadrature relationship may beprovided.

Referring to FIG. 11, in a third embodiment, an oscillator circuit 120comprises the first tank circuit T1 and the feedback stage F asdescribed in relation to the oscillator circuit 100 of FIG. 3, thefeedback stage F having a third feedback configuration. The first tankcircuit T1 generates at the first tank output 13, in response to thefirst oscillating drive voltage V_(D1) present at the first tank input12, the first oscillating tank voltage V_(T1) having a phase lagging aphase of the first oscillating drive voltage V_(D1) by 90°. In the thirdfeedback configuration, the feedback stage F comprises a phase shiftstage P arranged for applying a phase lag of 90°, and a first driver D1.The phase shift stage P is coupled to the input 17 of the feedback stageF for receiving the first oscillating tank voltage V_(T1) from the firsttank circuit T1. The phase shift stage P generates, at an output 14 ofthe phase shift stage P, and responsive to the first oscillating tankvoltage V_(T1), a first intermediate oscillating voltage V_(I1) having aphase lagging by 90° a phase of the first oscillating tank voltageV_(T1). The output 14 of the phase shift stage P is coupled to theoutput 18 of the feedback stage F via the first driver D1 whichgenerates, responsive to the first oscillating intermediate voltageV_(T1), the first oscillating drive voltage V_(D1) by applying signalinversion to the first intermediate oscillating voltage V_(I1). Due tothe 90° phase shift provided by the first tank circuit T1, the 90° phaseshift provided by the phase shift stage P, and the inversion provided bythe first driver D1, corresponding to a phase shift of 180°, the firstoscillating drive voltage V_(D1) has a phase that leads the phase of thefirst oscillating tank voltage V_(T1) by 90°, as required to sustainoscillation. The first oscillating tank voltage V_(T1) and the firstintermediate oscillating voltage V_(I1) differ in phase by 90°, andtherefore are available as quadrature-related oscillating signals.

Referring to FIG. 12, in a fourth embodiment, an oscillator circuit 130is identical to the third embodiment described with reference to FIG.11, except that the first tank circuit T1 is arranged to generate at thefirst tank output 13, in response to the first oscillating drive voltageV_(D1) present at the first tank input 12, the first oscillating tankvoltage V_(T1) having a phase leading a phase of the first oscillatingdrive voltage V_(D1) by 90°, and the first driver D1 does not applysignal inversion but generates, responsive to the first oscillatingintermediate voltage V_(I1), the first oscillating drive voltage V_(D1)in-phase with the first intermediate oscillating voltage V_(I1), withthe result that the first oscillating drive voltage V_(D1) has a phasethat leads the phase of the first oscillating tank voltage V_(T1) by90°, as required to sustain oscillation. The first oscillating tankvoltage V_(T1) and the first intermediate oscillating voltage V_(I1)differ in phase by 90°, and therefore are available asquadrature-related oscillating signals.

Referring to FIG. 13, a fifth embodiment, an oscillator circuit 140comprises the first tank circuit T1 and the feedback stage F asdescribed in relation to the oscillator circuit 100 of FIG. 3, thefeedback stage F having a fourth feedback configuration. The first tankcircuit T1 generates at the first tank output 13, in response to thefirst oscillating drive voltage V_(D1) present at the first tank input12, the first oscillating tank voltage V_(T1) having a phase lagging aphase of the first oscillating drive voltage V_(D1) by 90°. In the thirdfeedback configuration, the feedback stage F comprises a first phaseshift circuit P1, a second phase shift circuit P2, a first driver D1, asecond driver D2, and a second tank circuit T2. The first phase shiftcircuit P1 is coupled to the input 17 of the feedback stage F, andgenerates at an output 15 of the first phase shift circuit P1,responsive to the first oscillating tank voltage V_(T1), a firstintermediate oscillating voltage V_(I1) have a phase that lags the phaseof the first oscillating tank voltage V_(T1) by 90°. The output 15 ofthe first phase shift circuit P1 is coupled to a second drive node 22 ofthe second tank circuit T2 via the second driver D2 which generates,responsive to the first intermediate oscillating voltage V_(I1), asecond oscillating drive voltage V_(D2) in-phase with the firstintermediate oscillating voltage V_(I1). The second oscillating drivevoltage V_(D2) is delivered to the second drive node 22. The second tankcircuit T2 generates at a second tank output 23, in response to thesecond oscillating drive voltage V_(D2), a second oscillating tankvoltage V_(T2) having a phase lagging a phase of the second oscillatingdrive voltage V_(D2) by 90°. The second phase shift circuit P2 iscoupled to the second tank output 23 of the second tank circuit T2, andgenerates at an output 16 of the second phase shift circuit P2,responsive to the second oscillating tank voltage V_(T2), a secondintermediate oscillating voltage V_(I2) having a phase that lags thephase of the second oscillating tank voltage V_(T2) by 90°. The output16 of the second phase shift circuit P2 is coupled to the output 18 ofthe feedback stage F via the first driver D1 which generates, responsiveto the second intermediate oscillating voltage V_(I2), the firstoscillating drive voltage V_(D1) in-phase with the second intermediateoscillating voltage V_(I2). The first and second oscillating tankvoltages V_(T1), V_(T2) differ in phase by 180°, and so may be used asfirst and second signal components of a balanced oscillating signal. Thefirst oscillating drive voltage V_(D1) delivered from the output 18 ofthe feedback stage F has a phase that lags the phase of the firstoscillating tank voltage V_(T1) by 270°, or equivalently leads the phaseof the first oscillating tank voltage V_(T1) by 90°, as required tosustain oscillation.

Referring to FIG. 14, in a sixth embodiment, an oscillator circuit 150is identical to the fifth embodiment described with reference to FIG.13, except that the second driver D2 applies signal inversion to thefirst oscillating intermediate voltage V_(I1), such that the secondoscillating drive V_(D2) generated by the second driver D2 is 180°out-of-phase with respect to the first oscillating intermediate voltageV_(I1), and second tank circuit T2 is arranged to generate at the secondtank output 23, in response to the second oscillating drive voltageV_(D2) present at the second tank input 22, the second oscillating tankvoltage V_(T2) having a phase that lags a phase of the secondoscillating drive voltage V_(D2) by 90°. Consequently, the first andsecond oscillating tank voltages V_(T1), V_(T2) differ in phase by 180°,and so may be used as first and second signal components of a balancedoscillating signal, and the first oscillating drive voltage V_(D1) has aphase that leads the phase of the first oscillating tank voltage V_(T1)by 90°, as required to sustain oscillation.

Referring to FIG. 15, in a seventh embodiment, an oscillator circuit 160generates a pair of signals that have a quadrature relationship, andcomprises the first tank circuit T1 and the feedback stage F asdescribed in relation to the oscillator circuit 100 of FIG. 3, thefeedback stage F having a fifth feedback configuration. The first tankcircuit T1 generates the first oscillating tank voltage V_(T1) at thefirst tank output 13 in response to, the first oscillating drive voltageV_(D1) applied at the first drive node 12, and having a phase that lagsa phase of the first oscillating drive voltage V_(D1) by 90°. In thefifth feedback configuration, the feedback stage F comprises a secondtank circuit T2 having a second drive node 22 for applying a secondoscillating drive voltage V_(D2) to the second tank circuit T2, and asecond tank output 23 for delivering a second oscillating tank voltageV_(T2) from the second tank circuit T2. The second tank output 23 iscoupled to the output 18 of the feedback stage F via a first driver D1,and the second drive node 22 is coupled to the input 17 of the feedbackstage F via a second driver D2. The second driver D2 generates thesecond oscillating drive voltage V_(D2) 180° out-of-phase with the firstoscillating tank voltage V_(T1) by applying signal inversion the firstoscillating tank voltage V_(T1). The second tank circuit T2 generates asecond oscillating tank voltage V_(T2) at the second tank output 23 inresponse to the second oscillating drive voltage V_(D2) applied at thesecond drive node 22, and having a phase that lags a phase of the secondoscillating drive voltage V_(D2) by 90°. The first driver D1 generatesthe first oscillating drive voltage V_(D1) in response to, and in-phasewith, the second oscillating tank voltage V_(T2). Therefore, the firstoscillating drive voltage V_(D1) is generated in response to, andin-phase with, the first oscillating tank voltage V_(T1), as required tosustain oscillation. The second oscillating tank voltage V_(T2) is 180°out-of-phase with respect to the first oscillating tank voltage V_(T1),and consequently the first and second oscillating tank voltages V_(T1),V_(T2) are available to be used as first and seconds signal componentsof a balanced oscillating signal.

Referring to FIG. 16, in an eighth embodiment, an oscillator circuit 170is identical to the seventh embodiment described with reference to FIG.15, except that the first tank circuit T1 generates the firstoscillating tank voltage V_(T1) having a phase that leads a phase of thefirst oscillating drive voltage V_(D1) by 90°, and the second tankcircuit T2 generates a second oscillating tank voltage V_(T2) having aphase that leads a phase of the second oscillating drive voltage V_(D2)by 90°. Therefore, the first and second oscillating tank voltagesV_(T1), V_(T2) differ in phase by 90°, so have a quadraturerelationship, and the first oscillating drive voltage V_(D1) has a phasethat lags the phase of the first oscillating tank voltage V_(T1) by 90°,as required to sustain oscillation.

Referring to FIG. 17, in a ninth embodiment, an oscillator circuit 180is identical to the seventh embodiment described with reference to FIG.15, except that the first tank circuit T1 generates the firstoscillating tank voltage V_(T1) having a phase that leads a phase of thefirst oscillating drive voltage V_(D1) by 90°, and the second driver D2does not apply signal inversion, such that the second oscillating drivevoltage V_(D2) is in-phase with the first oscillating tank voltageV_(T1). Again, the first and second oscillating tank voltages V_(T1),V_(T2) differ in phase by 90°, so have a quadrature relationship, andthe first oscillating drive voltage V_(D1) has a phase that lags thephase of the first oscillating tank voltage V_(T1) by 90°, as requiredto sustain oscillation.

In some applications, an oscillator circuit is required that generates apair of signals that have a quadrature relationship, that is, differ inphase by 90°, and where both of the signals are required to be balanced,both having first and second signal components. In this case, foursignal components are required having phases 0°, 90°, 180° and 270°.Such an oscillator circuit has application in, for example, localoscillator signal generation in wireless communication apparatus.

Referring to FIG. 18, in a tenth embodiment, an oscillator circuit 190generates balanced quadrature-related oscillating signals, and comprisesthe first tank circuit T1 and the feedback stage F as described inrelation to the oscillator circuit 100 of FIG. 3, the feedback stage Fhaving a sixth feedback configuration. The first tank circuit T1generates the first oscillating tank voltage V_(T1) at the first tankoutput 13 in response to, the first oscillating drive voltage V_(D1)applied at the first drive node 12, and having a phase that lags a phaseof the first oscillating drive voltage V_(D1) by 90°. In the sixthfeedback configuration, the feedback stage F comprises a second tankcircuit T2 having a second drive node 22 for applying a secondoscillating drive voltage V_(D2) to the second tank circuit T2 and asecond tank output 23 for delivering a second oscillating tank voltageV_(T2) from the second tank circuit T2, a third tank circuit T3 having athird drive node 32 for applying a third oscillating drive voltageV_(D3) to the third tank circuit T3 and a third tank output 33 fordelivering a third oscillating tank voltage V_(T3) from the third tankcircuit T3, and a fourth tank circuit T4 having a fourth drive node 42for applying a fourth oscillating drive voltage V_(D4) to the fourthtank circuit T4, and a fourth tank output 43 for delivering a fourthoscillating tank voltage V_(T4) from the fourth tank circuit T4. Thefeedback stage F also comprises a first driver D1 having an input 703coupled to the fourth tank output 43 and an output 704 coupled to theoutput 18 of the feedback stage F and thereby to the first drive node12, a second driver D2 having an input 707 coupled to the input 17 ofthe feedback stage F and thereby to the first tank output 13, and anoutput 708 coupled to the second drive node 22, a third driver D3 havingan input 733 coupled to the second tank output 23 and an output 734coupled to the third drive node 32, and a fourth driver D4 having aninput 737 coupled to the third tank output 33 and an output 738 coupledto the fourth drive node 42. The first driver D1 generates the firstoscillating drive voltage V_(D1) responsive to, and in-phase with, thefourth oscillating tank voltage V_(T4). The second driver D2 generatesthe second oscillating drive voltage V_(D2) responsive to, and in-phasewith, the first oscillating tank voltage V_(T1). The third driver D3generates the third oscillating drive voltage V_(D3) responsive to, andin-phase with, the second oscillating tank voltage V_(T2). The fourthdriver D4 generates the fourth oscillating drive voltage V_(D4)responsive to, and in-phase with, the third oscillating tank voltageV_(T3). The second oscillating tank voltage V_(T2) has a phase that lagsthe phase of the first oscillating tank voltage V_(T1) by 90°, the thirdoscillating tank voltage V_(T3) has a phase that lags the phase of thesecond oscillating tank voltage V_(T2) by 90°, and the fourthoscillating tank voltage V_(T4) has a phase that lags the phase of thethird oscillating tank voltage V_(T3) by 90°, thereby providing twoquadrature-related balanced oscillating signals. The first oscillatingdrive voltage V_(D1) leads the first oscillating tank voltage V_(T1) by90°, as required to sustain oscillation.

A first variant of the oscillator circuit 190 described with referenceto FIG. 18 differs from the oscillator circuit 190 in that each of thefirst, second, third and fourth drivers D1, D2, D3, D4 provide signalinversion, such that the second oscillating drive voltage V_(D2) is 180°out-of-phase with the first oscillating tank voltage V_(T1), the thirdoscillating drive voltage V_(D3) is 180° out-of-phase with the secondoscillating tank voltage V_(T2), the fourth oscillating drive voltageV_(D4) is 180° out-of-phase with the third oscillating tank voltageV_(T3), and the first oscillating drive voltage V_(D1) is 180°out-of-phase with the fourth oscillating tank voltage V_(T4).

A second variant of the oscillator circuit 190 described with referenceto FIG. 18 differs from the oscillator 190 in that the first tankcircuit T1 generates the first oscillating tank voltage V_(T1) having aphase that leads the phase of the first oscillating drive voltage V_(D1)by 90°, the second tank circuit T2 generates the second oscillating tankvoltage V_(T2) having a phase that leads the phase of the secondoscillating drive voltage V_(D2) by 90°, the third tank circuit T3generates the third oscillating tank voltage V_(T3) having a phase thatleads the phase of the third oscillating drive voltage V_(D3) by 90°,and the fourth tank circuit T4 generates the fourth oscillating tankvoltage V_(T4) having a phase that leads the phase of the fourthoscillating drive voltage V_(D4) by 90°.

A third variant of the oscillator circuit 190 described with referenceto FIG. 18 differs from the oscillator circuit 190 in that each of thefirst, second, third and fourth drivers D1, D2, D3, D4 provide signalinversion, such that the second oscillating drive voltage V_(D2) is 180°out-of-phase with the first oscillating tank voltage V_(T1), the thirdoscillating drive voltage V_(D3) is 180° out-of-phase with the secondoscillating tank voltage V_(T2), the fourth oscillating drive voltageV_(D4) is 180° out-of-phase with the third oscillating tank voltageV_(T3), and the first oscillating drive voltage V_(D1) is 180°out-of-phase with the fourth oscillating tank voltage V_(T4). Inaddition, the first tank circuit T1 generates the first oscillating tankvoltage V_(T1) having a phase that leads the phase of the firstoscillating drive voltage V_(D1) by 90°, the second tank circuit T2generates the second oscillating tank voltage V_(T2) having a phase thatleads the phase of the second oscillating drive voltage V_(D2) by 90°,the third tank circuit T3 generates the third oscillating tank voltageV_(T3) having a phase that leads the phase of the third oscillatingdrive voltage V_(D3) by 90°, and the fourth tank circuit T4 generatesthe fourth oscillating tank voltage V_(T4) having a phase that leads thephase of the fourth oscillating drive voltage V_(D4) by 90°.

Each of the first, second and third variants of the oscillator circuit190 described with reference to FIG. 18 generates balancedquadrature-related oscillating signals.

Referring to FIG. 19, there is illustrated a preferred embodiment of thefirst, second, third and fourth drivers D1, D2, D3, D4 of the oscillatorcircuit 190 illustrated in, and described with reference to, FIG. 18.The first driver D1 comprises first and second transistors N1, N2 whichare n-channel CMOS transistors. The first transistor N1 has a drain N1 dcoupled to a first power supply rail 70 supplying a power supply voltageV_(dd1), a gate N1 g coupled to the input 703 of the first driver D1 bya first coupling capacitor C_(b1), and a source N1 s coupled to theoutput 704 of the first driver D1. The second transistor N2 has a drainN2 d coupled to the output 704 of the first driver D1, a source coupledto a second power supply rail 71 supplying a power supply voltageV_(ss1), and a gate N2 g coupled to the first power supply rail 70 by afirst resistor R1 for biasing. The third driver D3 comprises third andfourth transistors N3, N4 which are n-channel CMOS transistors. Thethird transistor N3 has a drain N3 g coupled to the first power supplyrail 70, a gate N3 g coupled to the third driver D3. The fourthtransistor N4 has a drain N4 d coupled to the output 734 of the firstdriver D1, a source N4 s coupled to the second power supply rail 71, anda gate N4 g coupled to the first power supply rail 70 by a secondresistor R2 for biasing.

Continuing to refer to FIG. 19, the second driver D2 comprises fifth andsixth transistors N5, N6 which are n-channel CMOS transistors. The fifthtransistor N5 has a drain N5 d coupled to a third power supply rail 72supplying a power supply voltage V_(dd2), which may be the same as thepower supply voltage V_(dd1), a gate N5 g coupled to the input 707 ofthe second driver D2 by a third coupling capacitor C_(b3), and a sourceN5 s coupled to the output 708 of the second driver D2. The sixthtransistor N6 has a drain N6 d coupled to the output 708 of the seconddriver D2, a source coupled to a fourth power supply rail 73 supplying apower supply voltage V_(ss2), which may be the same as the power supplyvoltage V_(ss1), and a gate N6 g coupled to the third power supply rail72 by a third resistor R3 for biasing. The fourth driver D4 comprisesseventh and eighth transistors N7, N8 which are n-channel CMOStransistors. The seventh transistor N7 has a drain N7 g coupled to thesecond power supply rail 72, a gate N7 g coupled to the input 737 of thefourth driver D4, and a source N7 s coupled to the output 738 of thefourth driver D4. The eighth transistor N8 has a drain N8 d coupled tothe output 738 of the fourth driver D4, a source N8 s coupled to thefourth power supply rail 73, and a gate N8 g coupled to the third powersupply rail 72 by a fourth resistor R4 for biasing.

The first coupling capacitor C_(b1), in conjunction with non-illustratedparasitic capacitances of the gates N1 g and N4 g of, respectively, thefirst and fourth transistors N1, N4, form a capacitive voltage dividerto reduce the amplitude of the voltage applied, in response to thefourth oscillating tank voltage V_(T4) present at the input 703 of thefirst driver D1, to the gates N1 g and N4 g of, respectively, the firstand fourth transistors N1, N4 to a tolerable value. Likewise, the secondcoupling capacitor C_(b2) in conjunction with non-illustrated parasiticcapacitances of the gates N2 g and N3 g of, respectively, the second andthird transistors N2, N3, form a capacitive voltage divider to reducethe amplitude of the voltage applied, in response to the secondoscillating tank voltage V_(T2) present at the input 733 of the thirddriver D3, to the gates N2 g and N3 g of, respectively, the second andthird transistors N2, N3 to a tolerable value. Similarly, the third andfourth coupling capacitors C_(b3), C_(b4) perform a corresponding roleto reduce the amplitude of the voltages applied to the gates N5 g, N6 g,N7 g, N8 g of the fifth, sixth, seventh and eighth transistors N5, N6,N7, N8.

In those described embodiments of the oscillator circuit which comprisemore than one tank circuit, the tank circuits have an equal, orsubstantially the same, resonance frequency, for example within 5%. Thiscontributes to high power efficiency. In particular, their respectiveinductive elements may have an equal, or substantially the same,inductance, and their respective capacitive elements may have an equal,or substantially the same, capacitance.

Each of the first, second, third and fourth drivers D1, D2, D3, D4 maybe linear or non-linear amplifiers, but preferably, for high powerefficiency, are arranged to switch, dependent on the voltage at theirrespective inputs relative to a threshold, alternatively between twodifferent voltage levels, which typically are power supply voltages.Therefore, the respective first, second, third and fourth oscillatingdrive voltages V_(D1), V_(D2), V_(D3), V_(D4) may have a square orrectangular waveform, or an approximately square or rectangular waveformhaving finite rise and fall times. The first, second, third and fourthdrivers D1, D2, D3, D4 are arranged to deliver power to the respectivefirst, second, third and fourth tank circuits T1, T2, T3, T4 in order tosustain oscillation. Although embodiments of the first, second, thirdand fourth drivers D1, D2, D3, D4 have been described with reference toFIG. 19 in relation to the oscillator circuit 190 described withreference to FIG. 18, and its variants, these embodiments may beemployed also in other of the disclosed oscillator circuits. Moreover,although embodiments of the first, second, third and fourth drivers D1,D2, D3, D4 have been described which comprise solely n-channel CMOStransistors, this is not essential, and variants comprising p-channelCMOS transistors and n-channel CMOS transistors may be employed instead.

Optionally, provision for tuning the frequency of oscillation may beadded to the disclosed oscillator circuits. For example, FIG. 20illustrates the oscillator circuit 160 described with reference to FIG.15, but with additional provision for tuning comprising a variablecapacitance element C_(V) coupled to the first tank output 13 via afirst additional capacitor C_(x), and coupled to the second tank output23 via a second additional capacitor C_(y). The first and secondadditional capacitors C_(x), C_(y) are included to attenuate the firstand second oscillating tank voltages V_(T1), V_(T2) applied to thevariable capacitance element C_(V) to a value that is tolerable by thevariable capacitance element C_(V). Depending on the voltage level thatcan be tolerated by the variable capacitance element C_(V), the firstand second additional capacitors C_(x), C_(y) may be omitted, with thevariable capacitance element C_(V) instead being coupled directly to thefirst and second tank outputs 13, 23 respectively. Typically, afrequency tuning range of about 10% may be provided by the variablecapacitance element C_(V).

FIG. 21 illustrates the phase noise of the oscillator circuit 190described with reference to FIG. 18, as a function of frequency offsetfrom the oscillation frequency, for the case where the inductive elementof each of the first, second, third and fourth tank circuits T1, T2, T3,T4 has an inductance of 0.5 nH, the oscillator circuit 190 is arrangedto oscillate at an oscillation frequency of 6 GHz, the voltage rail 14of each of the first, second, third and fourth tank circuits T1, T2, T3,T4 provides 0.6V, and the oscillator circuit 190 draws a current of 110mA. Graph a) in FIG. 21 represents the total phase noise, graph b)represents the contribution of thermal noise to the total phase noise,and graph c) represents the contribution of flicker noise to the totalphase noise. Despite the low supply voltage, a very low phase noise isobtained, for example, −150 dBc/Hz at 10 MHz offset from the oscillationfrequency. Such a low phase noise level would require a much largercapacitance and a much lower inductance in a parallel-resonanceoscillator, resulting in a much less robust design.

Referring to FIG. 22, a wireless communication device 900, such as amobile phone, comprises an antenna 910 coupled to an input of a lownoise amplifier 920 for amplifying a radio frequency (RF) signalreceived by the antenna 910. An output of the low noise amplifier 920 iscoupled to a first input 932 of a down-conversion stage 930 fordown-converting the amplified RF signal to baseband by mixing theamplified RF signal with quadrature-related components of a localoscillator signal present at a second input 934 of the down-conversionstage 930. An output 936 of the down-conversion stage 930 is coupled toan input 952 of a digital signal processor (DSP) 950 via ananalogue-to-digital converter (ADC) 940 that digitises the basebandsignal. The DSP 950 demodulates and decodes the digitised basebandsignal. The DSP 950 also generates, at an output 954 of the DSP 950, abaseband signal to be transmitted. The output 954 of the DSP 950 iscoupled to a first input 972 of an up-conversion stage 970 via adigital-to-analogue converter (DAC) 960. The up-conversion stage 970up-converts the baseband signal to RF for transmission by mixing thebaseband signal with quadrature-related components of the localoscillator signal present at a second input 974 of the up-conversionstage 970. An output 976 of the up-conversion stage 970 is coupled tothe antenna 910 via a power amplifier 980 that amplifies the RF signalfor transmission. The wireless communication device 900 comprises theoscillator circuit 100 described with reference to FIG. 3, which in thisembodiment generates the first oscillating tank voltage V_(T1) at thefirst tank output 13. The first tank output 13 of the oscillator circuit100 is coupled to an input 992 of a quadrature generation phase element990. The quadrature phase generation element 990 generates from thefirst oscillating tank voltage V_(T1) quadrature-related components ofthe local oscillator signal at a first output 994 and at a second output996 of the quadrature phase generation element 990. The first output 994of the quadrature phase generation element 990 is coupled to the secondinput 934 of the down-conversion stage 930, and the second output 996 ofthe quadrature phase generation element 990 is coupled to the secondinput 974 of the up-conversion stage 970. In applications where thelocal oscillator signal is required to be a balanced signal, theoscillator circuit 100 may employ any of the embodiments that generate abalanced oscillating signal, in particular the oscillator circuits 115,140, 150, 160 described with reference to FIGS. 10, 13, 14 and 15.

In a variant of the wireless communication device 900, the oscillatorcircuit 100 and the quadrature phase generation element 990 may bereplaced by one of the oscillator circuits 120, 130, 170, 180 describedwith reference to FIGS. 11, 12, 16 and 17 which generatequadrature-related oscillating signals or quadrature-related balancedoscillating signals.

Other variations and modifications will be apparent to the skilledperson. Such variations and modifications may involve equivalent andother features that are already known and which may be used instead of,or in addition to, features described herein. Features that aredescribed in the context of separate embodiments may be provided incombination in a single embodiment. Conversely, features that aredescribed in the context of a single embodiment may also be providedseparately or in any suitable sub-combination.

It should be noted that the term “comprising” does not exclude otherelements or steps, the term “a” or “an” does not exclude a plurality, asingle feature may fulfil the functions of several features recited inthe claims and reference signs in the claims shall not be construed aslimiting the scope of the claims. It should also be noted that where acomponent is described as being “arranged to” or “adapted to” perform aparticular function, it may be appropriate to consider the component asmerely suitable “for” performing the function, depending on the contextin which the component is being considered. Throughout the text, theseterms are generally considered as interchangeable, unless the particularcontext dictates otherwise. It should also be noted that the Figures arenot necessarily to scale; emphasis instead generally being placed uponillustrating the principles of the present invention.

1. An oscillator circuit comprising: a first tank circuit comprising aninductive element and a capacitive element coupled in series between avoltage rail and a first drive node; and a feedback stage coupled to afirst tank output of the first tank circuit and to the first drive node;wherein the feedback stage is arranged to generate, responsive to afirst oscillating tank voltage present at the first tank output, a firstoscillating drive signal at the first drive node in-phase with anoscillating tank current flowing in the inductive element and thecapacitive element, thereby causing the oscillator circuit to oscillatein a series resonance mode of the inductive element and the capacitiveelement.
 2. The oscillator circuit as claimed in claim 1, wherein thefeedback stage is arranged to generate the first oscillating drivesignal having a substantially rectangular waveform.
 3. The oscillatorcircuit as claimed in claim 1, wherein the first tank circuit isarranged to generate, responsive to the first oscillating drive signal,the first oscillating tank voltage in-phase with the first oscillatingdrive signal, and wherein the feedback stage comprises a first driverarranged to generate, responsive to the first oscillating tank voltage,the first oscillating drive signal in-phase with the first oscillatingtank voltage.
 4. The oscillator circuit as claimed in claim 3, whereinthe first tank circuit comprises a sensor device arranged to generatethe first oscillating tank voltage responsive to the first oscillatingtank current.
 5. The oscillator circuit as claimed in claim 4, whereinthe sensor device comprises one of a resistive element and a transformercoupled in series with the inductive element and the capacitive elementbetween the voltage rail and the first drive node.
 6. The oscillatorcircuit as claimed in claim 4, wherein the sensor device is magneticallycoupled to the inductive element for generating by magnetic inductionthe first oscillating tank voltage responsive to the first oscillatingtank current.
 7. The oscillator circuit as claimed in claim 4, whereinthe capacitive element is coupled between the first drive node and thefirst tank output and the inductive element is coupled between the firsttank output and the first voltage rail.
 8. The oscillator circuit asclaimed in claim 4 wherein the inductive element is coupled between thefirst drive node and the first tank output and the capacitive element iscoupled between the first tank output and the first voltage rail.
 9. Theoscillator circuit as claimed in claim 3, wherein the feedback stageincludes a feedback stage tank circuit and the first driver comprises:an input coupled to the feedback stage tank circuit; an output coupledwith the first drive node; a transistor having a gate, a source, and adrain, wherein the source is coupled with the output and the drain iscoupled with a power supply rail; and a coupling capacitor coupled withthe input and the gate.
 10. The oscillator circuit as claimed in claim1, wherein the first tank circuit is arranged to generate, responsive tothe first oscillating drive signal, the first oscillating tank voltageone hundred and eighty degrees out-of-phase with the first oscillatingdrive signal, and wherein the feedback stage comprises a first driverarranged to generate, responsive to the first oscillating tank voltage,the first oscillating drive signal one hundred and eighty degreesout-of-phase with the first oscillating tank voltage by applying signalinversion to the first oscillating tank voltage.
 11. The oscillatorcircuit as claimed in claim 10, wherein the feedback stage comprises: afeedback stage tank circuit having feedback stage tank circuit output,the feedback stage tank circuit coupled with the first driver; and avariable capacitance element coupled with the first tank output and thefeedback stage tank circuit output.
 12. The oscillator circuit asclaimed in claim 11, where wherein the feedback stage further comprises:a first capacitor coupled between the feedback stage tank circuit outputand the variable capacitance element; and a second capacitor coupledbetween the variable capacitance element and the first tank output. 13.The oscillator circuit as claimed in claim 1, wherein the first tankcircuit is arranged to generate, responsive to the first oscillatingdrive signal, the first oscillating tank voltage in-phase with the firstoscillating drive signal, and wherein the feedback stage comprises: asecond driver arranged to generate a second oscillating drive signal byapplying signal inversion to the first oscillating tank voltage; asecond tank circuit arranged to generate, responsive to the secondoscillating drive signal, a second oscillating tank voltage in-phasewith the second oscillating drive signal; and a first driver arranged togenerate the first oscillating drive signal by applying signal inversionto the second oscillating tank voltage.
 14. The oscillator circuit asclaimed in claim 1, wherein the first tank circuit is arranged togenerate, responsive to the first oscillating drive signal, the firstoscillating tank voltage one hundred and eighty degrees out-of-phasewith the first oscillating drive signal, and wherein the feedback stagecomprises: a second driver arranged to generate a second oscillatingdrive signal by applying signal inversion to the first oscillating tankvoltage; a second tank circuit arranged to generate, responsive to thesecond oscillating drive signal, a second oscillating tank voltagein-phase with the second oscillating drive signal; and a first driverarranged to generate the first oscillating drive signal in-phase withthe second oscillating tank voltage.
 15. The oscillator circuit asclaimed in claim 1, wherein the first tank circuit is arranged togenerate, responsive to the first oscillating drive signal, the firstoscillating tank voltage one hundred and eighty degrees out-of-phasewith the first oscillating drive signal, and wherein the feedback stagecomprises: a second driver arranged to generate, responsive to the firstoscillating tank voltage, a second oscillating drive signal in-phasewith the first oscillating tank voltage; a second tank circuit arrangedto generate, responsive to the second oscillating drive signal, a secondoscillating tank voltage one hundred and eighty degrees out-of-phasewith the second oscillating drive signal; and a first driver arranged togenerate, responsive to the second oscillating tank voltage, the firstoscillating drive signal in-phase with the second oscillating tankvoltage.
 16. The oscillator circuit as claimed in claim 1, wherein thefirst tank circuit is arranged to generate, responsive to the firstoscillating drive signal, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivesignal, and wherein the feedback stage comprises a phase shifting stagearranged to generate a first intermediate oscillating voltage byapplying a phase lag of ninety degrees to the first oscillating tankvoltage and the oscillator circuit further comprises a first driverarranged to generate the first oscillating drive signal by applyingsignal inversion to the first intermediate oscillating voltage.
 17. Theoscillator circuit as claimed in claim 1, wherein the first tank circuitis arranged to generate, responsive to the first oscillating drivesignal, the first oscillating tank voltage having a phase leading byninety degrees a phase of the first oscillating drive signal, andwherein the feedback stage comprises a phase shifting stage arranged togenerate a first intermediate oscillating voltage by applying a phaselag of ninety degrees to the first oscillating tank voltage, furthercomprising a first driver arranged to generate the first oscillatingdrive signal in response to, and in-phase with, the first intermediateoscillating voltage.
 18. The oscillator circuit as claimed in claim 1,wherein the first tank circuit is arranged to generate, responsive tothe first oscillating drive signal, the first oscillating tank voltagehaving a phase lagging by ninety degrees a phase of the firstoscillating drive signal, and wherein the feedback stage comprises: afirst phase shift circuit arranged to generate a first intermediateoscillating voltage by applying a phase lag of ninety degrees to thefirst oscillating tank voltage; a second driver arranged to generate,responsive to the first intermediate oscillating voltage, a secondoscillating drive signal in-phase with the first intermediateoscillating voltage, a second tank circuit arranged to generate,responsive to the second oscillating drive signal, a second oscillatingtank voltage having a phase lagging by ninety degrees a phase of thesecond oscillating drive signal; a second phase shift circuit arrangedto generate a second intermediate oscillating voltage by applying aphase lag of ninety degrees to the second oscillating tank voltage; anda first driver arranged to generate, responsive to the secondintermediate oscillating voltage, the first oscillating drive signalin-phase with the second intermediate oscillating voltage.
 19. Theoscillator circuit as claimed in claim 1, wherein the first tank circuitis arranged to generate, responsive to the first oscillating drivesignal, the first oscillating tank voltage having a phase lagging byninety degrees a phase of the first oscillating drive signal, andwherein the feedback stage comprises: a first phase shift circuitarranged to generate a first intermediate oscillating voltage byapplying a phase lag of ninety degrees to the first oscillating tankvoltage; a second driver arranged to generate a second oscillating drivesignal by applying signal inversion to the first intermediateoscillating voltage; a second tank circuit arranged to generate,responsive to the second oscillating drive signal, a second oscillatingtank voltage having a phase leading by ninety degrees a phase of thesecond oscillating drive signal; a second phase shift circuit arrangedto generate a second intermediate oscillating voltage by applying aphase lag of ninety degrees to the second oscillating tank voltage; anda first driver arranged to generate, responsive to the secondintermediate oscillating voltage, the first oscillating drive signalin-phase with the second intermediate oscillating voltage.
 20. Theoscillator circuit as claimed in claim 1, wherein the first tank circuitis arranged to generate, responsive to the first oscillating drivesignal, the first oscillating tank voltage having a phase lagging byninety degrees a phase of the first oscillating drive signal, andwherein the feedback stage comprises: a second driver arranged togenerate a second oscillating drive signal by applying signal inversionto the first oscillating tank voltage; a second tank circuit arranged togenerate, responsive to the second oscillating drive signal, a secondoscillating tank voltage having a phase lagging by ninety degrees aphase of the second oscillating drive signal; and a first driverarranged to generate, responsive to the second oscillating tank voltage,the first oscillating drive signal in-phase with the second oscillatingtank voltage.
 21. The oscillator circuit as claimed in claim 1, whereinthe first tank circuit is arranged to generate, responsive to the firstoscillating drive signal, the first oscillating tank voltage having aphase leading by ninety degrees a phase of the first oscillating drivesignal, and wherein the feedback stage comprises: a second driverarranged to generate a second oscillating drive signal by applyingsignal inversion to the first oscillating tank voltage; a second tankcircuit arranged to generate, responsive to the second oscillating drivesignal, a second oscillating tank voltage having a phase leading byninety degrees a phase of the second oscillating drive signal; and afirst driver arranged to generate, responsive to the second oscillatingtank voltage, the first oscillating drive signal in-phase with thesecond oscillating tank voltage.
 22. The oscillator circuit as claimedin claim 1, wherein the first tank circuit is arranged to generate,responsive to the first oscillating drive signal, the first oscillatingtank voltage having a phase leading by ninety degrees a phase of thefirst oscillating drive signal, and wherein the feedback stagecomprises: a second driver arranged to generate, responsive to the firstoscillating tank voltage, a second oscillating drive signal in-phasewith the first oscillating tank voltage; a second tank circuit arrangedto generate, responsive to the second oscillating drive signal, a secondoscillating tank voltage having a phase lagging by ninety degrees aphase of the second oscillating drive signal; and a first driverarranged to generate, responsive to the second oscillating tank voltage,the first oscillating drive signal in-phase with the second oscillatingtank voltage.
 23. The oscillator circuit as claimed in claim 1, whereinthe first tank circuit is arranged to generate, responsive to the firstoscillating drive signal, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivesignal, and wherein the feedback stage comprises: a second driverarranged to generate, responsive to the first oscillating tank voltage,a second oscillating drive signal in-phase with the first oscillatingtank voltage; a second tank circuit arranged to generate, responsive tothe second oscillating drive signal, a second oscillating tank voltagehaving a phase lagging by ninety degrees a phase of the secondoscillating drive signal; a third driver arranged to generate,responsive to the second oscillating tank voltage, a third oscillatingdrive signal in-phase with the second oscillating tank voltage; a thirdtank circuit arranged to generate, responsive to the third oscillatingdrive signal, a third oscillating tank voltage having a phase lagging byninety degrees a phase of the third oscillating drive signal; a fourthdriver arranged to generate, responsive to the third oscillating tankvoltage, a fourth oscillating drive signal in-phase with the thirdoscillating tank voltage; a fourth tank circuit arranged to generate,responsive to the fourth oscillating drive signal, a fourth oscillatingtank voltage having a phase lagging by ninety degrees a phase of thefourth oscillating drive signal; and a first driver arranged togenerate, responsive to the fourth oscillating tank voltage, the firstoscillating drive signal in-phase with the fourth oscillating tankvoltage.
 24. The oscillator circuit as claimed in claim 1, wherein thefirst tank circuit is arranged to generate, responsive to the firstoscillating drive signal, the first oscillating tank voltage having aphase leading by ninety degrees a phase of the first oscillating drivesignal, and wherein the feedback stage comprises: a second driverarranged to generate, responsive to the first oscillating tank voltage,a second oscillating drive signal in-phase with the first oscillatingtank voltage; a second tank circuit arranged to generate, responsive tothe second oscillating drive signal, a second oscillating tank voltagehaving a phase leading by ninety degrees a phase of the secondoscillating drive signal; a third driver arranged to generate,responsive to the second oscillating tank voltage, a third oscillatingdrive signal in-phase with the second oscillating tank voltage; a thirdtank circuit arranged to generate, responsive to the third oscillatingdrive signal, a third oscillating tank voltage having a phase leading byninety degrees a phase of the third oscillating drive signal; a fourthdriver arranged to generate, responsive to the third oscillating tankvoltage, a fourth oscillating drive signal in-phase with the thirdoscillating tank voltage; a fourth tank circuit arranged to generate,responsive to the fourth oscillating drive signal, a fourth oscillatingtank voltage having a phase leading by ninety degrees a phase of thefourth oscillating drive signal; and a first driver arranged togenerate, responsive to the fourth oscillating tank voltage, the firstoscillating drive signal in-phase with the fourth oscillating tankvoltage.
 25. The oscillator circuit as claimed in claim 1, wherein thefirst tank circuit is arranged to generate, responsive to the firstoscillating drive signal, the first oscillating tank voltage having aphase lagging by ninety degrees a phase of the first oscillating drivesignal, and wherein the feedback stage comprises: a second driverarranged to generate a second oscillating drive signal by applyingsignal inversion to the first oscillating tank voltage; a second tankcircuit arranged to generate, responsive to the second oscillating drivesignal, a second oscillating tank voltage having a phase lagging byninety degrees a phase of the second oscillating drive signal; a thirddriver arranged to generate a third oscillating drive signal by applyingsignal inversion to the second oscillating tank voltage; a third tankcircuit arranged to generate, responsive to the third oscillating drivesignal, a third oscillating tank voltage having a phase lagging byninety degrees a phase of the third oscillating drive signal; a fourthdriver arranged to generate a fourth oscillating drive signal byapplying signal inversion to the third oscillating tank voltage; afourth tank circuit arranged to generate, responsive to the fourthoscillating drive signal, a fourth oscillating tank voltage having aphase lagging by ninety degrees a phase of the fourth oscillating drivesignal; and a first driver arranged to generate the first oscillatingdrive signal by applying signal inversion to the fourth oscillating tankvoltage.
 26. The oscillator circuit as claimed in claim 1, wherein thefirst tank circuit is arranged to generate, responsive to the firstoscillating drive signal, the first oscillating tank voltage having aphase leading by ninety degrees a phase of the first oscillating drivesignal, and wherein the feedback stage comprises: a second driverarranged to generate a second oscillating drive signal by applyingsignal inversion to the first oscillating tank voltage; a second tankcircuit arranged to generate, responsive to the second oscillating drivesignal, a second oscillating tank voltage having a phase leading byninety degrees a phase of the second oscillating drive signal; a thirddriver arranged to generate a third oscillating drive signal by applyingsignal inversion to the second oscillating tank voltage; a third tankcircuit arranged to generate, responsive to the third oscillating drivesignal, a third oscillating tank voltage having a phase leading byninety degrees a phase of the third oscillating drive signal; a fourthdriver arranged to generate a fourth oscillating drive signal byapplying signal inversion to the third oscillating tank voltage; afourth tank circuit arranged to generate, responsive to the fourthoscillating drive signal, a fourth oscillating tank voltage having aphase leading by ninety degrees a phase of the fourth oscillating drivesignal; and a first driver arranged to generate the first oscillatingdrive signal by applying signal inversion to the fourth oscillating tankvoltage.
 27. A wireless communication device comprising: an oscillatorcircuit comprising: a first tank circuit comprising an inductive elementand a capacitive element coupled in series between a voltage rail and afirst drive node; and a feedback stage coupled to a first tank output ofthe first tank circuit and to the first drive node; wherein the feedbackstage is arranged to generate, responsive to a first oscillating tankvoltage present at the first tank output, a first oscillating drivesignal at the first drive node in-phase with an oscillating tank currentflowing in the inductive element and the capacitive element, therebycausing the oscillator circuit to oscillate in a series resonance modeof the inductive element and the capacitive element.
 28. A method ofoperating an oscillator circuit, the oscillator circuit comprising afirst tank circuit comprising an inductive element and a capacitiveelement coupled in series between a first voltage rail and a first drivenode, the method comprising generating, responsive to a firstoscillating tank voltage present at a first tank output, a firstoscillating drive signal at the first drive node, wherein the firstoscillating drive signal is in-phase with a first oscillating tankcurrent flowing in the inductive element and the capacitive element,thereby causing the oscillator to oscillate in a series resonance modeof the inductive element and the capacitive element.